Synthesis of (meth)acrylate water-borne latexes using amino-acid based surfactants: effect of surfactant on film properties

The rapidly increasing concern over environmental changes necessitates the employment of ecologically friendly surfactants for use in emulsion polymerisation without, however, compromising the latex stability or the properties of the cast films. To this end, three series of water-borne, lightly cross-linked latexes based on methyl methacrylate and butyl acrylate were prepared by free radical emulsion polymerisation. 1,4-Butanediol diacrylate served as the cross-linker. Each of the latex series was stabilised by one anionic, amino-acid based surfactant, namely: sodium lauroyl sarcosinate (SLSar), sodium myristoyl sarcosinate (SMSar) and sodium lauroyl glutamate (SLGlu). For comparison purposes, latexes stabilised by sodium dodecyl sulfate (SDS) were also prepared. Within each family, the monomer-to-surfactant molar ratio was varied systematically, whereas the monomer and initiator contents were kept constant in all cases. The hydrodynamic radii (R-h) and the radii of gyration (R-g) of the particles were found to systematically increase with increasing monomer-to-surfactant molar ratio. Films prepared from the SLSar and SDS stabilized latexes were investigated in terms of their optical and thermomechanical properties using transmittance experiments, differential scanning calorimetry, tensile strength and creep experiments. Optimal thermomechanical properties were observed for a particular monomer-to-surfactant molar ratio. Moreover, for the same monomer-to-surfactant molar ratio, the SLSar-based films exhibit remarkable resistance to breaking compared to their SDS counterparts that are relatively fragile.